1. Field of Invention
The present invention relates in general to an over-temperature protection circuit, and more particularly to a circuit for thermal protection in audio power amplifier and a method thereof.
2. Related Art
The purpose of the audio amplifier is to reconstruct the input audio signal to output to the element for generating audio. The frequency range of the audio is about 20 Hz to 20 KHz. Thus, the audio amplifier must have a good frequency response in the abovementioned frequency range. According to the different applications, the necessary powers of the audio amplifier are greatly different. For example, the application of milli-watts may be earphone, the application of watts may be speaker for TV or PC, the application of tens of watts may be automotive audio system or home theater stereo, and the application of hundreds of watts may be stereo for auditorium hall or Movie Theater.
FIG. 1 illustrates a block diagram depicting an audio amplifier circuit in a conventional art. Referring to FIG. 1, the audio amplifier includes a pre-amplifier 101, an output stage amplifier 102 and a feedback circuit 103. The pre-amplifier 101 is used for amplifying the weak input signal Vin to output an amplified output signal Va. Since the voltage amplified output signal Va still cannot drive the speaker 104, the output stage amplifier 102 is used for performing a current amplifying to the amplified output signal Va such that the speaker 104 can be driven. The feedback circuit 103 is used for increasing the stability of the whole circuit and improving the frequency response according to the principle of negative feedback.
Since there is huge current flowing through the output stage amplifier 102, the power consumption thereof is also huge, the output stage amplifier 102 generally would attach a heat sink. However, the heat sink may not completely absorb the heat generated by the output stage amplifier 102, Thus, the damage of the output stage amplifier 102 commonly occurs when the output stage amplifier 102 is overheat. In order to solve the problem, a temperature detecting mechanism is provided. When the temperature is greater than a threshold, the audio amplifier would be shut down to prevent the damage of the audio amplifier. However, users would have a uncomfortable feeling on user's hearing.